U.S. patent number 4,456,793 [Application Number 06/386,722] was granted by the patent office on 1984-06-26 for cordless telephone system.
This patent grant is currently assigned to Bell Telephone Laboratories, Incorporated. Invention is credited to William E. Baker, Fritz E. Froehlich, Hans G. Mattes.
United States Patent |
4,456,793 |
Baker , et al. |
June 26, 1984 |
Cordless telephone system
Abstract
The present key telephone system comprises cordless telephone
stations (FIGS. 6 and 7) which communicate over a line-of-sight
transmission end link (276 or 277). The system further comprises a
central controller (101) for switching communications between the
cordless stations and to the message network. The central
controller does not provide any station to transmission channel
concentration. Concentration occurs in the bidding by a cordless
station for access to a channel provided by the line-of-sight
transmission end link. A particular number of transmission channels
are provided by the line-of-sight end link which are bid for by any
practical number of cordless stations. Subsystem controllers (104)
are provided in a large cordless key telephone system. The
subsystem controller reformats data for transmission between the
central controller (101) and a cordless station. A unique code
identifies a cordless station so that the allocation of a new
channel to a cordless station may occur automatically when a
cordless station is detected within the boundaries of a new
subsystem.
Inventors: |
Baker; William E. (Holmdel,
NJ), Froehlich; Fritz E. (Little Silver, NJ), Mattes;
Hans G. (Indianapolis, NJ) |
Assignee: |
Bell Telephone Laboratories,
Incorporated (Murray Hill, NJ)
|
Family
ID: |
23526772 |
Appl.
No.: |
06/386,722 |
Filed: |
June 9, 1982 |
Current U.S.
Class: |
379/56.3;
379/165; 455/438; 455/417; 379/93.14; 379/92.01; 398/103; 398/100;
398/121 |
Current CPC
Class: |
H04B
10/40 (20130101); H04B 10/1149 (20130101); H04W
84/16 (20130101); H04M 1/737 (20130101); H04W
36/00 (20130101); H04W 74/00 (20130101); H04W
72/04 (20130101); H04W 8/26 (20130101); H04W
4/18 (20130101) |
Current International
Class: |
H04B
10/10 (20060101); H04M 1/72 (20060101); H04M
1/737 (20060101); H04Q 7/26 (20060101); H04M
001/72 (); H04M 003/22 () |
Field of
Search: |
;179/99R,82,2EB,2EA,99M,81R ;455/3733,606,607
;340/311.1,825.06,825.07,825.08 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Proceedings of the IEEE vol. 67, No. 11, Nov. 1979, "Wireless
In-House Data Communication via Diffuse Infrared Radiation," pp.
1474-1486. .
Optical Spectra, Dec., 1979, "IBM Uses Infrared to Transmit Data,"
pp. 16, 18, 19 & 20. .
IEEE, Aug., 1978, "Infrared Communication for In-House
Application," pp. 132-138..
|
Primary Examiner: Schreyer; Stafford D.
Attorney, Agent or Firm: Jackson; T. H. Newman; H. L.
Claims
What is claimed is:
1. A cordless telephone system
characterized by
a central controller (101) for switching telephone communications,
means at the central controller for transmitting and receiving a
plurality of coded message signals, the coded message signals
transmitted and received over transmission channel means (410,
411), the transmission channel means connecting the central
controller to a particular number of transceivers adaptably
dispersed so as to divide a location of the telephone system into a
number of cells, each cell having at least one transceiver, the
system further including at least one cordless telephone station
having a particular unique address, the cordless telephone station
communicating with the transceiver over an optical transmission end
link, the cordless telephone station being relocatable from a first
cell to a second cell within the telephone system, the central
controller providing telephone service to the cordless telephone
station during movement of the station from the first cell to the
second cell essentially without interruption over a particular
assigned channel of the transmission channel means.
2. A cordless telephone system as recited in claim 1
further characterized by
a plurality of subsystem controllers (104), each subsystem
controller controlling telephone communications and having memory
(304a) for storing the addresses of cordless telephone stations
(107, 108, or 110) located within cells (201-207) associated with
the subsystem controller, each subsystem controller being connected
to the central controller (101) by transmission and control channel
means (103), each subsystem controller particularly polling the
cordless telephone stations located within its associated cells,
each cordless telephone station responding to the polling by
transmitting a present signal, the subsystem controller reporting
the address of a nonresponding cordless telephone station over
control channel means (521) to the central controller, the central
controller responding to the report by requesting over control
channel means all other subsystem controllers to request a response
from the nonresponding cordless telephone station.
3. A cordless telephone system as recited in claim 1 or 2
further characterized in that
the cordless telephone station comprises a key telephone station
set (107).
4. In a cordless telephone station system comprising a central
controller, a number of subsystem controllers connected to the
central controller by transmission channel means (410, 411, 520)
and control channel means (412, 521) and a plurality of
transceivers (105, 106, 109) located at cell locations and
connected to the subsystem controllers by transmission channel
means (113), a method of identifying movement of a cordless
telephone station from the control of one subsystem controller to
the control of another subsystem controller comprising the steps
of: assigning a particular unique address to each cordless
telephone station; the subsystem controller periodically polling
each cordless telephone station within a subsystem according to its
particular unique address; in the event a cordless telephone
station fails to respond with a present signal, the subsystem
controller transmitting over control channel means to the central
controller for temporary storage in memory the particular unique
address of the nonresponding station; the central controller
causing other subsystem controllers to grab an available frame of
information to be transmitted toward its associated optical
transceivers, the other subsystem controllers polling their
associated cordless telephone stations according to the particular
unique address of the nonresponding cordless telephone station; a
subsystem controller, upon locating a missing station, reporting to
the central controller the particular unique address of the located
station.
5. A method of identifying a movement of a station from one
subsystem to another as recited in claim 4 additionally comprising
the steps of assigning in temporary memory a high priority to a
particular nonresponding station when first reported missing; with
each successive polling by other subsystem controllers for the
particular nonresponding station, reducing the priority level for
the nonresponding station such that, as the priority level
decreases, the frequency of search for the nonresponding station
also decreases.
6. A method of identifying movement of a station from one subsystem
to another as recited in claim 4 additionally comprising the step
of polling the stations of subsystem controllers adjacent to the
reporting subsystem controller before polling subsystem controllers
situated at a greater distance from the reporting subsystem
controller.
7. Cordless station apparatus for receiving an optical signal
modulated by a data and telephone signal, the apparatus comprising
means (623) for dividing a clock signal by a particular number to
derive a time slot counting function; counting means (601)
responsive to the dividing means; decoding means (602) responsive
to the counting means, the decoding means providing a telephone
channel counting signal to a channel selection means (603) and data
transfer means (618) for providing data to a microprocessor (700),
the microprocessor updating an associated memory responsive to the
transfer of data.
8. Cordless station apparatus as recited in claim 7, the data
transfer means (618) having first and second modes of operation,
the first mode for transferring cordless station update data to
microprocessor the (700), the second mode for providing new channel
data to the channel selection means (603).
9. An electronic key telephone station set
characterized by
a microprocessor (700) comprising first and second output leads or
ports (701, 702), the first and second output leads or ports for
scanning a key or button field (710) in a first mode of operation
and for lighting lamps of a lamp field (730) in a second mode of
operation.
10. A cordless telephone system comprising:
a central controller for switching telephone communications, a
plurality of subsystem controllers connected to the central
controller, each subsystem controller being connected to a
particular number of transceivers, the transceivers being dispersed
so as to divide a location of the telephone system into a number of
cells, each subsystem controller being associated with at least one
cell and each cell having at least one transceiver, a plurality of
cordless telephone stations each having a unique address, the
cordless telephone stations being relocatable from a first cell to
a second cell within the telephone system, each subsystem
controller polling the cordless telephone stations located within
its associated cell, the subsystem controller reporting the address
of a nonresponding cordless telephone station to the central
controller, the central controller responding to the report by
requesting all of the subsystem controllers to request a response
from the nonresponding cordless telephone station.
11. A cordless telephone system as in claim 10 wherein the cordless
telephone stations are connected to an associated transceiver by an
optical link.
12. A cordless telephone system as in claim 10 wherein the central
controller provides telephone service to the cordless telephone
stations during movement of a station from the first cell to the
second cell without interruption.
13. A cordless telephone system as in claim 10 wherein each
subsystem controller is connected to the central controller by
transmission and control channel means, the subsystem controller
reporting the address of a nonresponding telephone station over the
control channel means and the central controller responding to the
report by requesting over the control channel means all other
subsystem controllers to request a response from the nonresponding
telephone station.
14. A cordless telephone system as in claim 10 wherein each
subsystem controller comprises a processor having memory and
encoding and decoding circuitry, the subsystem controller
reformatting data received from a cordless telephone station for
transmission to the central controller and reformatting data
received from the central controller for transmission to the
cordless telephone station.
15. A cordless communication system comprising:
a central controller for switching communications, a plurality of
subsystem controllers connected to the central controller, each
subsystem controller having a plurality of terminals associated
therewith, each terminal having a unique address, each subsystem
controller periodically polling the terminals associated therewith,
the subsystem controller reporting the address of a nonresponding
terminal to the central controller, the central controller
responding to the report by requesting all of the subsystem
controllers to request a response from the nonresponding
terminal.
16. In a cordless communication system comprising a plurality of
subsystem controllers, a method of permitting movement of a
terminal from the control of one subsystem controller to the
control of another subsystem controller comprising the steps
of:
assigning a particular unique address to each terminal; causing
each subsystem controller to periodically poll each terminal that
responded to the previous poll according to its unique address; in
the event a terminal fails to respond, transmitting to other
subsystem controllers the unique address of the nonresponding
terminal; causing the other subsystem controllers to poll for the
nonresponding terminal according to its unique address; and causing
a subsystem controller, upon receiving a response from the terminal
to assume control over the terminal.
Description
TECHNICAL FIELD
This invention relates to key telephone systems and, more
particularly, to a key telephone system employing infrared
transmission and comprising cordless telephone station sets.
BACKGROUND OF THE INVENTION
Cordless telephone station sets are commercially available which
employ a radio transmission link between a portable hand-held unit
and a fixed base station unit. Some of these telephone sets operate
over a particular radio frequency channel. In cellular mobile
radio, the mobile set bids for access to a plurality of radio
frequency channels. Access to channels is provided by a centralized
controller through a transceiver at a cell site. The problem with
radio telephone systems generally is the limited availability of
radio frequency spectrum, the undesirability of interference
between transceivers operating at similar frequencies, and, hence,
the insecurity of any communications.
To overcome these problems, cordless telephone sets have been
proposed which employ line-of-sight transmission which may be
defined as transmission at frequencies above approximately one
gigahertz. In particular, the safety to the user and other
considerations have pointed development in the area of cordless
telephony towards infrared transmission.
It has been reported that a cordless infrared telephone set has
been designed at Siemens Aktiengesellschaft, Munich, West Germany.
The set comprises a wall-mounted stationary unit and a hand-held
telephone set equipped with a dialing keyboard and a control
keyboard of three keys. A user may use the hand-held set anywhere
in a room, unconfined by cords. Interference with transmission to
wall-mounted stationary units by sunlight and other infrared
sources is overcome to a degree by mounting the stationary unit
near or on the ceiling of a room and by employing
infrared-reflecting window panes which are often installed to save
energy in modern buildings.
It has also been reported that a data communications system has
been developed at IBM Zurich Research Laboratory which incorporates
a plurality of cordless data terminals capable of operation at 125
Kbits/s. It is further reported that a 125 Kbits/s optical data
transmission link has been built and a switched in-house data
network designed which comprises a host and cluster controllers
connected by conventional house cable. The cluster controller is
connected by house cable to a number of rooms where a ceiling
mounted satellite controls access to a number of data terminals
over the optical link. Communications are reasonably secure in
accordance with the above discoveries. Telephone rewiring of a
premises is required when telephone stations are moved from one
room to another.
In U.S. Pat. No. 4,275,385, a personnel locater system is disclosed
comprising portable transmitters. Each transmitter is personal to
an individual who carries it and transmits a unique code. A master
processor is capable of identifying the vicinage of a transmitter
as it identifies which ceiling mounted receiver has reported the
code. In this manner, local alerters in the vicinage of the
received transmission can alert a needed individual. Only one way
transmission is disclosed. A portable transmitter, in accordance
with the disclosed system, is capable of movement outside the
boundaries of a room, unlike the communications devices of the IBM
and Siemens disclosures.
It is generally believed advantageous to maintain maximum
flexibility in telephone systems. It is desirable that office and
telephone station rearrangements occur without expensive
rearrangements of conventional telephone house cable. Records as to
features, services and locations of particular telephones within a
particular system should be centrally maintainable without human
intervention. Once a premises is equipped with a plurality of
ceiling mounted transceivers, no further intervention should be
required when a telephone is moved within the network. A portable
telephone station set should be capable of being carried about a
premises. In the process of being moved from room to room, the
portable set should permit an on-going telephone conversation to
continue without interference or concern about the confidentiality
of the communication.
Furthermore, it is well known that a one channel to one station
ratio is uneconomical and impractical in operation. A means for
allocating line-of-sight transmission channels among a number of
cordless stations is required for the practical implementation of a
cordless key telephone system.
SUMMARY OF THE INVENTION
The problems and limitations of the prior art are overcome by the
principles of the present cordless key telephone system employing
infrared transmission. The cordless telephone station apparatus of
the present system may comprise single line telephone sets or
multiline key telephone sets, data terminals, facsimile devices or
other types of communication devices. At least the single line and
small key telephone sets are portable and battery-powered and may
be carried about a premises during an on-going telephone
conversation without fear of interference or security of
communications.
For a sufficiently large number of stations, a central controller
is provided for switching communications among cordless stations
associated with a plurality of subsystem controllers and to or from
the direct distance dialing network. A subsystem controller
provides a particular number of channels for communicating with any
practical number of cordless telephone stations, a feature of the
present system being its means for allocating channels of a
line-of-sight transmission end link. Traffic studies suggest that,
with a normal mix of data and analog telephone stations, a fifty
channel subsystem is capable of supporting five hundred
stations.
The line-of-sight transmission end link connects a cordless
telephone station and a transceiver which may be mounted in the
ceiling. The transceiver is connected to the subsystem controller
by an optical fiber link. The optical signal is demodulated and
decoded at the location of the subsystem controller. In an
alternative embodiment, demodulation may occur at the location of
the ceiling mounted transceiver and a coaxial cable link may
connect the transceiver to the subsystem controller.
A premises is divided into a plurality of rooms, hereinafter
referred to as cells, which may be optically isolated from one
another. A long, angular hallway may be a cell. Ceiling mounted
transceivers are dispersed about a cell such as a hallway so that
nominal transmission distances are not exceeded. A single room cell
normally requires only one transceiver.
A subsystem of the present cordless system comprises a number of
proximately located cells. For example, one floor of an office
building constitutes a reasonable subsystem.
Within the memory of the central controller are stored unique codes
for each subsystem and station within the subsystem. Particular
information regarding each station including its current or last
reported location, its features, current subsystem assignment, main
line number, pick-up station numbers, traffic data and other
information is stored in temporary memory of the central
controller. The central controller may be either a space or time
division controller known in the art.
In connection with a rearrangement of cordless stations, the
central controller periodically and automatically causes a
subsystem controller to poll for its assigned stations by their
unique station codes. A station normally responds with a present
signal if it is within its assigned subsystem. If a station is
missing and not within an assigned subsystem, the central
controller causes adjacent subsystems to poll for missing stations.
Once detected, a missing station's new subsystem data is
automatically stored in central controller memory. In this manner,
a rearrangement of stations is accomplished without human
intervention.
Once a channel is allocated for transmission between a station and
its assigned subsystem controller for a telephone communication, a
cordless portable station may be hand-carried from cell to cell
without interrupting an on-going telephone conversation. At the
perimeters of a subsystem, a channel in an adjacent subsystem may
be obtained pursuant to the previously described process of
locating a "missing" phone. Passing from one cell in one subsystem
to a cell in an adjacent subsystem causes only a brief, hardly
perceptible interruption or click.
In the subsequently described embodiment of the present invention,
modulated infrared transmission is suggested for the line-of-sight
transmission end link for safety and other reasons. The modulated
infrared transmission is accomplished in the station to
ceiling-mounted transceiver direction at baseband modulation
frequencies between ten and fourteen megahertz and, in the
transceiver to station direction at sixteen to twenty megahertz,
thus permitting a four megahertz bandwidth in each direction. A
fifteen megahertz modulation signal is employed for frame
synchronization.
A frame of data for transmission over the optical end link
comprises eighty-three time slots, fifty of which time slots
comprise fifty one way communication channels. The communications
signal for transmission over a time slot channel is sampled at
eight kilohertz and the resulting sample is transmitted as a
frequency burst where the frequency is a linear function of the
sampled voltage.
Depending on the direction of transmission and the particular
station type and features, the thirty-three remaining time slots
comprise various categories of data. In the subsystem controller to
station direction, the data comprises a unique station code, its
corresponding subsystem identifier, a field code and designator
for, for example, channel assignment data, error check bits at the
end of data, and a framemark to signify the beginning of data.
Responsive to a polling request, a cordless station transmits
toward the subsystem controller the following data: button and lamp
status change data, switchhook status, power status as, for
example, after a low battery detection check, a present signal, and
framemark and error check bits.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a pictorial representation of how a large system in
accordance with the present invention is physically constructed
within the confines of a telephone customer's premises;
FIG. 2 is a pictorial representation of one floor arrangement for
the premises depicted in FIG. 1, the depicted floor arrangement
being an exemplary subsystem of a large cordless key telephone
system in accordance with the present invention;
FIG. 3 is a general block diagram of a large cordless key telephone
system employing infrared transmission in accordance with the
present invention;
FIG. 4 is a block diagram of a central controller of the space
division switching type which may be employed in the present
cordless key telephone system;
FIG. 5 is a block diagram of one embodiment of a subsystem
controller which may be employed in the present cordless key
telephone system;
FIGS. 6 and 7 are block diagrams of a cordless key telephone
station set employed with the present invention;
FIG. 8 is a depiction of a frame of data for transmission from a
subsystem controller transceiver to a cordless station; and
FIG. 9 is a depiction of a frame of data for transmission from a
cordless station to a subsystem controller.
DETAILED DESCRIPTION
Referring to FIG. 1, a pictorial representation is shown of how a
large cordless key telephone system in accordance with the present
invention is physically constructed within the confines of a
telephone customer's premises. A customer's premises may be a
large, multistoried office building 100, a particular floor 120 of
which is shown in cut-away view. A floor 120 comprises a number of
rooms 108 or 111.
Line-of-sight transmission frequencies above approximately one
gigahertz are suggested for transmission within rooms 108 and 111.
Safety and other factors currently tend to limit the choice of
line-of-sight frequencies for cordless transmission to those in the
infrared region. This is not to suggest that other frequency bands
above one gigahertz may not be applied in the present invention.
Advances in technology at other line-of-sight frequencies which are
safe to users may disclose new bands of line-of-sight frequencies
which may be employed.
Windows 114 of building 100 may be constructed of reflective
materials at the line-of-sight frequency band of interest. With
infrared frequencies, reflective glass is energy efficient and,
when used with the present invention, preserves confidentiality of
communications. The present system has a high modulation
coefficient and a correspondingly high signal-to-noise ratio.
Each room 108 or 111 is constructed so as to incorporate ceiling
mounted optical transceivers 105, 106, or 109. Telephone
communications terminals employed in the present system may
comprise computer data terminals 107, hand-held portable telephones
110, key telephone sets 112 or other types of telephone terminals
known in the art. The telephone terminals of the present invention
are distinguished in their lack of telephone cabling. Since large
computer data terminal 107 consumes considerable power, it must be
located proximate to an alternating current power outlet. Despite
this limitation, computer data terminal 107 may be moved anywhere
within the present cordless key telephone system without the
assistance of telephone installation personnel.
Key telephone set 112 comprises a hold button, multiline pick-up
capability and most other features currently known in the art.
Visual indicators, such as lamps or light emitting diodes, and keys
mounted on the set 112 identify to the user thereof the status of
the lines and features. By efficient power design, key telephone
sets of the present system may be battery-operated.
Hand-held portable telephone set 110 has line pick-up capacity and
is capable of being moved freely from room 111 to room 108 even
during an ongoing telephone communication. In its idle state,
hand-held set 110 should be rested upon a charging stand for
restoration of its associated batteries after each use.
Telephone terminals 107, 110 and 112 are equipped with optical
transceivers for optical communication at line-of-sight
transmission frequencies with ceiling mounted transceivers 105,
106, and 109. Even when idle, key telephone station 112 is
frequently polled so that visual indicator status information can
be updated, the indicator status relating to the busy status of the
multiline pick-up capability of set 112.
The ceiling mounted transceivers 105, 106, and 109 should be
located so as to optimize optical transmission. In room 108 or room
111, the ceiling mounted transceiver may be mounted in a dark
corner either on the ceiling or high on a wall. Fluorescent light
fixtures are less likely to interfere with transmission. Yet, while
one might presume that the three surfaces of walls at a corner tend
to focus the light beams, it has been discovered that they do not
guide optical transmission and reception. A further problem with
corner-mounted transceivers is that a door or other optical barrier
is likely to be present which blocks or otherwise limits
transmission and reception. Therefore, centrally located
ceiling-mounted transceivers have proven viable and promote optimum
transmission.
In a sufficiently small room 108, only one transceiver 109 is
required. In a large room 111 or a long angular corridor, a
plurality of optical transceivers may be required. In the depicted
example, transceivers 105 and 106 are most conveniently spaced at
some distance less than the maximum transmission distance of the
transceiver. In angular corridors, a transceiver must be so located
as to encompass transmissions from the vertex of the angle.
A floor having a plurality of transceivers most conveniently forms
a subsystem of a large cordless key telephone system. All
transceivers within a subsystem are connected to a subsystem
controller 104 by optical fiber cable or coaxial cable 113
depending on the capabilities incorporated into transceivers 105,
106, or 109.
In particular if the transceiver serves an optical repeater
function, the connecting media is most conveniently optical fiber.
If the transceiver serves a greater function, that is, one of
transduction from large bandwidth energy to large bandwidth
electrical energy, then the connecting media is most conveniently
coaxial cable.
Of the above alternatives, the connecting media most conveniently
employed is optical fiber. Thus, the functions of transduction,
modulation, and coding occur at the location of the subsystem
controller 104. Subsystem controller 104, in addition to
transmission circuitry, comprises a processor having permanent and
semipermanent memory. For each telephone station it serves, it
stores in semipermanent memory a particular unique address code,
the latest transmitted and received button and light status data,
and transmission channel assignment data. Fifty optical
transmission channels for communications data are provided to each
transceiver within a subsystem. No switching is performed by
subsystem controller 104. All fifty transmission channels are
connected to a central controller 101 over a telephone house cable
and bus 103. In other words, no concentration between lines and
channels occurs at subsystem controller 104. Concentration or
channel allocation in the present system occurs when a telephone
station bids for an optical channel of its associated subsystem
controller. Channel allocation will be more particularly discussed
in the subsequent discussion of FIGS. 5, 6, 7, 8, and 9.
Between subsystem controller 104 and each transceiver, the
modulated optical signal comprises both telephone and data
channels. Between subsystem controller 104 and central controller
101, fifty cable pairs are used for the telephone information and
other leads of cable 103 are employed for a central
controller/subsystem controller bus. Control and data information
flow back and forth over the bus between the central controller and
subsystem controller.
The central controller 101 is an electronic space division
switching system comprising permanent and semipermanent memory. It
may be a microprocessor, in particular, a 16 bit microprocessor
known commercially as an Intel Corp. 8086. In performing its
switching function, it is capable of connecting any one of the
fifty channels of one subsystem 104 to any other channel of that
subsystem or to any channel of any other subsystem. In addition,
central controller 101 controls incoming and outgoing calls to a
telephone central office over trunk cable pairs 102.
Traffic studies for the present system indicate that each subsystem
for controlling fifty transmission channels may conveniently
comprise five hundred stations given a normal mix of data terminals
107, hand-held portable telephone sets 110, key telephone sets 112,
and other types of telephone station apparatus. For a large office
building, central controller 101 may be engineered to handle a
large number of subsystems 104.
Referring now to FIG. 2, a pictorial representation is shown of one
floor arrangement for the premises depicted in FIG. 1. The depicted
floor arrangement represents one exemplary subsystem of a large
cordless key telephone system in accordance with the present
invention.
Subsystem 200 comprises cells 201 through 207. Cells 202 through
207 are individual rooms while cell 201 is a corridor connecting
the rooms. The rooms have open or closed portals 280 through
287.
All optical transceivers 210, 211, 212, 220, 230, 240, 250, 260,
261, 270, and 271 are arranged geometrically without particular
concern to the construction of the rooms or corridors. If a wall is
knocked down and relocated and the intertransceiver distance kept
small enough, there likely will be no requirement to ever relocate
optical transceivers. In other words, while the maximum length of
an optical transmission link may be a hundred feet or more, the
design of subsystem 200 is neither dependent on that distance nor
on the present and future location of optical boundaries such as
walls. Proper choice of a geometric arrangement of transceivers
depends on permanent features of the floor arrangement such as
column locations, plumbing facilities, stairwells, and elevator
shafts.
Considering cells 202 and 205, they are, for example, typical one
person offices. Their distinctions reside in the location of their
cordless telephones 221 and 251. Cells 203 and 204 are offices
where there are more than one cordless telephone. The cordless
telephones 231-233 and 241-242 may likely be battery powered key
telephone sets.
Large office areas such as cells 206 and 207 may comprise a
combination of various types of cordless telephone apparatus. Such
apparatus as data terminals may have to be located next to
alternating current outlets.
Referring particularly to cell 207, various kinds of transmissions
may occur between a station and a ceiling mounted transceiver. For
example, telephone station 273 may communicate in a line-of-sight
path 277 to transceiver 270 or via a reflected path 276. An
infinite number of reflected paths are conceivable. In addition,
telephone station 273 communicates with any other transceiver not
blocked by an optical barrier of some sort. Problems caused by
delayed and attenuated reflections or transmissions to other
transceivers are solved by zero crossing techniques known in the
art and will be particularly addressed in the discussion of FIGS. 6
and 7. Since portals such as portal 280 may be left open, temporary
communication may be established over link 278 for the brief period
the portal is left open. The problem presented thereby, however, is
no different than the multiple transceiver reception problem
mentioned above.
Referring to FIG. 3, a general block diagram of a large key
telephone system is shown in accordance with the present invention.
The first digit of reference characters for elements depicted in
this and subsequent figures indicate where the depicted element
first appears.
A central controller 101 comprises program memory 301b for storage
of call processing, maintenance, traffic, feature, and other
algorithms required for operation of the present system. Temporary
memory 301a records the current association between telephone
terminal apparatus 107, 110, and 112 and subsystem controller 104
as well as for all other subsystem controllers. In addition,
temporary memory records the call processing status of all lines,
channels, trunks, dial detection circuits and service circuits,
their traffic usage data, and maintenance status. Central
controller 101 is connected to a telephone central office by trunk
cable 102 and to subsystem controller 104 by telephone house cable
103. All other subsystem controllers are similarly connected to
central controller 101.
Telephone house cable 103 comprises fifty two-way communication
channels and a central controller/subsystem controller bus. The bus
provides a two way data channel between central controller 101 and
subsystem controller 104.
Subsystem controller 104 comprises program memory 304b for storage
of transmission data channel control algorithms. These algorithms
operate responsive to the operation of associated telephone station
apparatus 107, 110, or 112 to provide data to central controller
101 over its subsystem controller bus 103. The data comprises line
status data, power status data, channel request data, present
signal data, and acknowledgement data that ordered tasks have been
performed. The algorithms operate responsive to the control of
central controller 101 to provide telephone station apparatus 107,
110, or 112 with channel assignment and polling data comprising
particular unique telephone set data and subsystem data. In
addition, these algorithms comprise maintenance programs which may
be operated during idle periods.
Subsystem controller 104 also comprises temporary memory 304a for
maintaining current the various data described above. The subsystem
controller serves to terminate optical fiber cable pairs 305, 306,
and 309 and all other optical fiber cable pairs to associated
transceivers. At the terminus of the optical fiber cable pairs is
an optical multiplex port capable of transmitting and receiving an
optical signal associated with a particular number of optical fiber
cable pairs. The number of optical multiplex ports provided by a
particular subsystem controller is determined by the number of
optical fiber cable pairs and associated optical transceivers.
Several stages of ports connected in tandem may be required in
large subsystems. The result of such an arrangement is that a
transmit port and a receive port are provided to which are
connected in tandem optical to electrical signal transducers,
modulation and demodulation circuits, and encoding and decoding
circuits.
Optical transceiver 105 and all other transceivers 106 through 109
comprise optical repeater, detection and transmission circuitry. A
two way optical channel 307 or other channels 308 and 309 are
provided between a particular optical transceiver 105 and any
stations within optical transmission boundaries such as stations
112, 107, and 110, respectively.
CENTRAL CONTROLLER
Referring to FIG. 4, a more particularized block diagram of a
central controller is shown than is provided by either FIG. 1 or
FIG. 3. In particular, it is appropriate to recognize that central
controller 101 is most conveniently an electronic space division
switch generally known in the art which operates in much the same
way as those not employed in a cordless environment.
When a station in subsystem 401 goes off hook, data is provided to
the central controller over controller/subsystem controller bus 412
of the service request and of the code of the first idle channel
410 or 411 from channels 1 through 50 at bus port 412a. Central
controller 101 then seeks to locate an idle dial detection circuit
404. If one is available, central controller 101 arranges the
connection of the idle channel to the idle dial detection circuit.
The connection, for example, of channel 1, leads 410, to dial
detection circuit 1, leads 441, is temporarily preserved in
temporary memory 301a. Simultaneously, central controller 101
signals subsystem 401 over bus 412 to change the channel status of
the allocated channel from reserved to busy. The selected dial
detection circuit 404 then causes dial tone to be provided over the
assigned channel to the calling line requesting service, signifying
to the user that dialing may begin. At the completion of dialing,
central controller 101 recognizes the nature of the service request
and searches for either an idle central office trunk or arranges an
intrasystem call over an intrasystem trunk.
The more complicated call is the intrasystem call so that call will
be discussed in detail. From temporary memory 301a, central
controller 101 obtains the last location of the dialed line.
Assuming for a moment the last location of the dialed line is
within subsystem 401 where the call originated, a request for
assignment of another idle channel is transmitted to subsystem 401
over bus 412. If another subsystem controller such as subsystem
controller 402 is associated with the called line, then a request
is made over bus 422 for an idle channel.
Following the progress of an intrasystem call to subsystem
controller 402, assignment data of the first idle channel 420 or
421 is returned over bus 422. Consequently, central controller 101
signals subsystem 402 to change the status of the allocated channel
to busy. Then, an idle intrasystem trunk circuit 403 is located and
a switching path to the trunk reserved in temporary memory 301a.
Thereafter, central controller 101 causes the release of the
connection to the selected dial detection circuit 404 and connects
the calling party to the called party through the intrasystem trunk
403. In accordance with techniques known in the art, the call is
supervised for an on-hook indication by central controller 101.
Upon the occurrence of an on-hook condition, subsystem controller
401 and 402 are alerted over buses 412 and 422, respectively to
return assigned channel status to idle. Simultaneously, the network
connection temporarily stored in temporary memory 301a is
erased.
The intrasystem trunk circuit 403 comprises a channel bridging
capability. This bridging capability is frequently employed because
a key telephone station is likely to share the same line as another
station. For example, one calling or called line of an intrasystem
call may appear upon key telephone sets located in the same or
different subsystems. The central controller 101 recognizes a
change of switchhook status of a station to be added to an ongoing
call and, as a result, bridges the new station into the ongoing
call at the intrasystem trunk circuit 403. Service circuits 406
normally provided by central controller 101 are for providing
standard tones such as busy tones and special features such as
conferencing in accordance with generally known techniques.
It can be seen from the above discussion that central controller
101 is practically identical in its operation with controllers
employed in a wholly wired environment. Accordingly, there is no
difficulty in providing, if desired, wired telephone station
apparatus 407. Many of the advantages of the present system are
defeated with the addition of telephone wiring; however, it is
important to note that wiring of a premises is not precluded.
SUBSYSTEM CONTROLLER
Referring now to FIG. 5, there is shown a block diagram of one
embodiment of a subsystem controller which may be employed in the
present cordless key telephone system. The subsystem controller is
connected to the central controller 101 by a house cable comprising
fifty channel pairs 520 of telephone tip and ring leads and a
central controller/subsystem controller bus 521. Processor 501 of
the subsystem controller receives and transmits data to the central
controller 101 over bus 521. In order to maintain a synchronous
relationship among subsystem controllers, bus 521 to processor 501
and to all other subsystem processors comprises clock signal leads
in addition to data leads. Data is transmitted and received in
parallel data format in the depicted embodiment.
Processor 501 is preferably a microprocessor such as an Intel Corp.
sixteen bit 8086. Processor 501 has a read/write memory which is
allocatable into permanent storage 304b for algorithms and
temporary storage 304a for call processing and other data.
Processor 501 controls the data encoding and decoding functions of
encoder 502 and decoder 503, respectively. In answering service
requests from calling stations, processor 501 operates responsive
to data received from the calling stations on input port 524.
Responsive to data received from the central controller, processor
501 provides updated lamp status, polling, and other data over
output port 523 to encoder 502. Other leads of ports 523 and 524
are for controlling the encoding and decoding of data.
A fifteen megahertz clock 511 is provided for synchronizing the
encoding and decoding of data. Data transmitted from the station to
subsystem controller is decoded from the ten to fourteen megahertz
band. Data transmitted in the subsystem controller to station
direction is encoded into the sixteen to twenty megahertz band.
Fifty two-wire-to-four-wire conversion circuits 530 are required
between the outputs of the encoder and decoder and the fifty pair
house cable 520. The separate directions of optical transmission
are rejoined at the conversion circuitry 530.
Modulator 504 is connected to the serial data output stream 525 of
encoder 502. It in turn provides modulating signal 527 for driving
optical driver 506. Optical driver 506 provides a modulated
infrared signal on single optical fiber 529 at the input to optical
multiplex port 508. At optical port 508, a plurality of amplified
identical outputs are provided responsive to input signal 529. At
optical connector 510, the resultant fibers are joined into
transmit and receive fiber optic pairs. Each fiber optic pair then
connects the optical connector 510 to a transceiver.
In the station to subsystem controller direction, the receive fiber
of an optical fiber cable pair is connected at optical connector
510 to optical demultiplex port 509. There the resulting optical
signals are summed and amplified. The output signal 530 operates a
photoresponsive diode or other device of receiver 507. Its baseband
output signal 528 is demodulated at demodulator 505. Data stream
526 is provided at decoder 503. Decoder 503 provides service
request and other data to processor 501 over leads 524 and
telephone data to the conversion circuits 530 over leads 522.
It may be seen from the above discussion that the subsystem
controller performs no line to channel concentration function. Its
purpose is to translate data into appropriate format for
transmission in either of two directions: toward the station or
toward the central controller. In the direction toward the station,
the subsystem controller operates responsive to a central
controller request. It constructs a serial data stream from fifty
channels of telephone information and from data received over bus
521 and from data in its temporary memory 304a. Frames of
communicative data are constructed in accordance with the
subsequent discussion of FIG. 8.
Such functions in a small cordless system environment, for example,
less than five hundred lines, can be provided at the location of
the central controller. Thus, in a small cordless key telephone
system, no separate PG,20 subsystem controllers are required. The
functions may be integrated into the design of central controller
101 and accomplished by it.
In the direction toward the central controller, the subsystem
controller operates responsive to frames of data transmitted by the
cordless stations. The data transmitted by the station is in the
format subsequently discussed in FIG. 9. The subsystem controller,
having polled a station, learns that it is "present," and of a
change from on-hook to off-hook status if its status has changed
and locates an idle channel. The subsystem controller then alerts
the central controller over bus 521 of the status change and the
reserved assignment of the previously idle channel. To do so, it
must consult its temporary memory 304a, first, to recognize the
change of status from on-hook to off-hook, then, to reserve the
first idle channel of the fifty potentially available channels.
CORDLESS STATION APPARATUS
Cordless station apparatus for application with the present key
telephone system is disclosed in pertinent part in FIGS. 6 and 7.
Telephone transmitter and receiver apparatus is not shown because
the design of such apparatus is well known. One important caveat is
that power conserving apparatus should be used wherever possible.
For example, electret transmitters and receivers, light emitting
diode or liquid crystal displays, and energy conserving touch
sensitive keyboards should be employed. Also, custom integrated
circuit technology is applied wherever possible in the present
circuit.
One custom integrated circuit 600 shown in FIG. 6 comprises many
logic and circuit elements including lateral redundancy check
circuit 605, decoder 602, time slot counter 601, channel selector
603, and serial to parallel shift register and logic circuit 604.
External to the custom integrated circuit 600 of FIG. 6 are shown
clock and divide logic circuit 623, infrared receiver 620,
synchronization recovery circuit 621, data recovery circuit 622,
zero crossing counter and analog decoder 626, encoder and modulator
circuit 625 and infrared transmitter 624. Many of these latter
elements comprise active filter components which may be designed in
accordance with switched capacitor filter CMOS integrated circuit
technology.
Processor 700, shown in FIG. 7, is most conveniently a three port,
eight bit microprocessor. One such microprocessor which may be
employed is an Intel Corp. 80C48. The CMOS circuitry of the 80C48
promotes energy efficiency. Port A comprises eight leads for data
input and output. Port B comprises five scanning leads for scanning
a five by eight key field 710 and for operating lamp drivers 720
for operating a five by eight lamp field 730. The three remaining
leads of port B provide a lateral redundancy check lead 619, a
phone select control lead 631 to encoder/modulator circuit 625, and
a data mark lead 614 from decoder circuit 602 for strobing the
microprocessor 700 to read data on bus 618.
Processor 700 generally operates responsive to a polling request
for data received at infrared receiver 620 (FIG. 6). Data recovery
circuit 622 extracts the polling and other data such as lamp
lighting data from the demodulated and decoded output of infrared
receiver 620. A serial data stream is provided to shift register
604 and to zero crossing counter and analog decoder 626. Read/write
lead 612 from decoder 602 indicates to shift register 604 when to
output or input data on bus 618. Data bus 618 is thus employed to
provide data in parallel format to port A of processor 700 shown in
FIG. 7. At the same time as data is shifted into microprocessor
700, the data is also shifted on leads 618A into the lateral
redundancy check circuit 605 which, responsive to decoder 602,
signals the processor 700 on lead 619 if there is an error so that
microprocessor 700 may ignore the data of port A and await an
error-free transmission.
Bus 618 is employed for two other purposes. Bus 618 is employed for
the purpose of outputting button data to shift register 604. The
button data is converted to serial format by register 604 and a
serial data stream is provided to encoder and modulator circuit 625
for transmission.
Processor 700 also employs bus 618 during a floating mode to load
channel allocation or assignment data on leads 618B into channel
selector circuit 603. In this manner, the cordless station is
enabled to decode the appropriate telephone message channel data at
zero crossing counter and analog decoder 626 as well as to time
slot multiplex a voice sample into an appropriate time slot channel
at encoder modulator 625.
Frame synchronization for incoming data from infrared demodulation
and decoder circuit 620 is provided by frame synchronization
recovery circuit 621. In particular, a frame mark is provided by
means of a phase reversal appearing in the first two time slots of
a frame. Recognition of the bit reversal by means of an active tank
filter at fifteen megahertz causes the resetting of clock and
divide logic circuit 623 over reset lead 607. Clock and divide
circuit 623 provides a time slot counting function output of 1.5
microseconds to time slot counter 601 over clock lead 606. When a
new frame of eighty three time slots is recognized at circuit 621,
it is clear that time slot counter 601 has reached a count of 83
time slots for the previously transmitted frame. Lead 607 is, thus,
also used to reset time slot counter 601. Count control leads 609
indicate to decoder circuit 602 when the time slots allocated to
data have been entered into shift register 604. Responsive to this
event, decoder 602 alerts shift register 604 on inhibit lead 611 to
inhibit the serial shifting of data. Time slot counter 601 also
indicates to channel selector 603 a time slot count on lead 608
representative of the fifty time slots reserved for telephone voice
sample data. The fifty channel count begins responsive to a command
on start count lead 615 from decoder 602.
Microprocessor 700 (FIG. 7) in accordance with techniques known in
the art scans for off-hook and on-hook status as well as for keypad
signaling and line button status. Its highest priority is to
immediately respond to an incoming polling request; however, it
also performs matrix scanning and visual indicator or lamp lighting
functions. Five leads 701 from port B of microprocessor 700 poll
key or button field 710 one row at a time. The eight leads of port
C provide input to microprocessor 700 as to which columns of key
field 710 have been actuated. Key field 710 may comprise a
signaling keypad, a key field for line pickup, as well as the
switchhook contact of the present cordless set.
For activating light emitting diodes or lamps, more than one lead
of port B may be actuated at a time. Port C is then employed for
outputting a column indication to current sink 740. The
simultaneous actuation of a lamp driver 720 and a current sink 740
causes the lighting of a lamp in lamp field 730. In similar
fashion, a subsequent concurrent actuation of a lamp driver and
current sink causes their associated lamp to extinguish. A flashing
algorithm can be implemented by use of a clock of microprocessor
700. The scanning algorithm of microprocessor 700 is temporarily
interrupted for performing lamp lighting algorithms.
Microprocessor 700 also actuates encoder and modulator 625 (FIG. 6)
over phone select lead 631 for insuring that a voice sample is
transmitted in an appropriate time slot at transmitter 624. The
audio signal output 630 is sampled at an eight kilohertz rate as
clocked by phone select lead 631. The resulting sample is sent as a
frequency burst within the allocated time slot channel provided by
channel select leads 616. The frequency burst in accordance with
known techniques is a linear function of the sampled voice signal
voltage.
In the receive direction, data recovery circuit 622 provides the
data output to zero crossing counter and analog decoder 626.
Channel selector circuit 603 provides the counter 626 with the
allocated channel number of the received telephone data. The voice
output 627 of the zero crossing counter and decoder 626 is provided
to a telephone speaker or receiver of a handset. Zero crossing
counter 626 automatically accounts for reflected transmissions and
transmissions received from more than one transceiver. Decoder 503
of FIG. 5 likewise employs a zero crossing counting technique to
provide a relatively noise-free output.
An exemplary frame of data for transmission in the subsystem
controller to cordless station direction is shown in FIG. 8. Other
time slot allocations may be employed which may be more or less
efficient and which recognize more or fewer transmission channels,
subsystems, and cordless telephone stations. It is believed that
one ordinarily skilled in the art may vary the suggested format in
accordance with their particular design requirements.
Choice of an eight kilohertz sampling rate for the voice sample at
lead 630 results in a 125 microsecond duration for each frame. As
has been previously discussed, the time slot counting function has
been selected at 750 nanoseconds and the time slot size is
approximately 1.5 microseconds or double the counting function to
account for accurate zero crossing counting, transmission delays,
and noise. Eighty three time slots are thus provided in total of
which fifty are reserved for telephone voice data.
The first two time slots of data are reserved for a frame mark
which, in the present key telephone system is accomplished by the
previously discussed phase reversal recognized by frame
synchronization recovery circuit 621. The next four time slots
indicate to the station set the subsystem where the cordless set is
currently located. The next thirteen time slots are reserved for
the unique address of a polled cordless station. These time slots
provide sufficient capacity for polling over eight thousand
telephones, a very large key telephone system.
The next ten time slots comprise two elements, a field designator
of four time slots and a data field of six time slots. The field
designator may be used to indicate to processor 700 what kind of
data the field comprises. For example, an entry of value zero in
the field designator may indicate that the date field comprises the
channel assignment, six time slots being sufficient to identify a
channel number between one and fifty.
The last four time slots are for checking for errors in the data
time slots. Any kind of parity or other error checking techniques
known in the art may be employed. An LRC check is suggested.
Referring briefly to FIG. 6, these four time slots are associated
with the report on leads 618A to LRC check circuit 605 where an
error report is generated on lead 619.
An exemplary frame of data for transmission in the cordless station
to subsystem controller direction is shown in FIG. 9. As the data
which must flow in this direction is less demanding of time slots,
only twenty four time slots of thirty three possible slots are
employed.
The first two time slots are employed for a framemark. The next
eight may represent a distinctive "present" signal which indicates
to a subsystem controller that the station scanned on previous
received frame is still located within a subsystem and has not
moved to a new subsystem. The distinctive code may be, for example,
10101010.
The next eight time slots are for button status. A maximum size key
field for the cordless station set is thus presumed to comprise
sixty-four switchable elements. In the discussion of FIGS. 6 and 7
depicting one cordless station set of the present invention, a
practical, maximum key field size of forty elements was
suggested.
The switchhook status for the actuated line of the key field
appears in the next time slot. If the battery is low in the
cordless set, the subsystem controller may be informed in the next
time slot. The last four data time slots are reserved for error
checking.
AUTOMATIC LOCATION OF MISSING CORDLESS STATIONS
Referring now to all the previously introduced figures, the
operation of the present system in automatically locating missing
cordless stations will be explained in detail. A cordless station
is determined missing whenever it fails to respond or is precluded
from responding when it is polled by central controller 101.
Missing stations thus include "in-service" stations which have
moved from one subsystem to another during the transistory period
between the last time they were polled and the present. The missing
in-service station may be involved in an on-going call or currently
idle when it is moved.
Missing stations also may include those which are "out-of-service."
In order to take a cordless station out of service, its power may
be removed. It may be placed in a closet or drawer where any
transmission from it is thwarted. The out-of-service cordless phone
is missing because it cannot respond with a present signal when
polled.
A cordless phone in the system is polled, during an on-going call,
approximately every 100 milliseconds. It is also useful to poll
in-service stations at this same rate during their idle periods in
order to detect changes in cordless station switchhook status and,
similarly, to report indicator lamp or light emitting diode status
changes to the cordless station.
Polling an out-of-service station at a 100 millisecond interval is
not necessary. The station which is out-of-service will be detected
quickly and may be placed on a low priority out-of-service polling
list in memory 301a of controller 101.
A cordless station is first polled by its unique station code in
the last subsystem stored in temporary memory 301a. In large
systems where there are more than two subsystems, adjacent
subsystems are polled first. It is presumed that the missing
station will likely be found there and searching only adjacent
subsystems frees all other subsystems to respond quickly to
stations which are in service. If the missing station does not
respond from within an adjacent subsystem, all other subsystems are
then requested to poll for the missing station. Accordingly, an
out-of-service phone will not report a "present" signal in three
successive attempts to locate it. A first attempt is made to locate
the missing phone in its assigned subsystem. If the attempt is
unsuccessful, an attempt is made to locate it in adjacent
subsystems, and lastly in all other subsystems.
The out-of-service phone will be identified as out-of-service after
a maximum of three hundred to four hundred milliseconds. The
out-of-service phone's unique code is placed along with a clock
time indication on an out-of-service list in temporary memory 301a.
The out-of-service phone is polled less frequently than the
in-service phone to conserve processing time for in-service
telephones. For example, the out-of-service phone may be polled
every second or even less frequently.
An out-of-service phone list may be provided by central controller
101 to telephone personnel for maintenance or billing purposes.
Because of the automatic reporting of out-of-service phones, a
considerable savings in requirements for maintenance and other
telephone personnel is anticipated with the present system. Of
course, the major advantage in savings comes from the automatic
rearrangement of in-service phones.
An in-service missing phone is detected in a new subsystem within
the time frame that an out-of-service phone is identified as
out-of-service, namely, after one hundred to three hundred
milliseconds maximum. The one hundred to three hundred millisecond
identification interval applies whether the in-service phone is
idle or involved in an on-going call.
If the phone is involved in an on-going call, an idle channel must
be immediately requested in the subsystem the missing, now found,
phone has moved to. The new channel is then bridged to the
connected central office trunk or intrasystem trunk held in network
memory 301a and the old channel released. Altogether the movement
of a station involved in an on-going call to a new subsystem may
create a switching delay of as long as one more cycle time or a
total maximum delay of three hundred to four hundred
milliseconds.
In an office rearrangement, where phones are permanently moved from
one subsystem to another, phone data is automatically updated in
memory 301a. The cordless phones are moved in such a rearrangement
without the intervention of maintenance or other personnel
resulting in a considerable savings of expenses normally associated
with telephone rearrangements.
* * * * *